Sex

The responses of male and female broilers to available lysine concentrations in the diet have been published by Thomas et al. (1977). Viewed in terms of dietary concentrations of total lysine, two growth response curves are apparent (Fig. 14.6) implying genuine differences in lysine utilization between males and females. Indeed, having arrived at this conclusion, Thomas et al. (1977) developed two regression equations for lysine requirements of male and female broilers. However, when the responses are considered as a function of daily lysine intake (Fig. 14.7) similarities in lysine utilization are seen. Thus, an intake of 600 mg day-1 would support equivalent growth rates in both males and females.

39 r

"O

300 400 500 600

Lysine intake (mg day-1)

Fig. 14.5. Daily weight gain and lysine intake of chicks injected with saline (o) or with immunogens in the form of E. coli lipopolysaccharide (•), S. typhimurium lipopolysaccharide (▲), or heat-killed S. aureus (A). Additional groups of chicks (■) received the three immunogens in rotation. (Source of data: Klasing and Barnes, 1988.)

300 400 500 600

Lysine intake (mg day-1)

Fig. 14.5. Daily weight gain and lysine intake of chicks injected with saline (o) or with immunogens in the form of E. coli lipopolysaccharide (•), S. typhimurium lipopolysaccharide (▲), or heat-killed S. aureus (A). Additional groups of chicks (■) received the three immunogens in rotation. (Source of data: Klasing and Barnes, 1988.)

It is consistently recorded that amino acid requirements, expressed as proportions of the diet, decrease with age (see National Research Council, 1994). D'Mello (1983) summarized published estimates for the SAA requirements of turkeys of different ages and these are reproduced in Table 14.1. A selection of the response data of Murillo and Jensen (1976) and of Behrends and Waibel (1980) are shown in Fig. 14.8. Expressed in these terms, there is little doubt that dietary requirements do decline with age. Of some concern, however, are the wide discrepancies in recommendations offered by different authors. Viewed in terms of dietary concentrations, the responses in Fig. 14.8 and the estimates in Table 14.1 appear irreconcilable. However, a different and more reassuring pattern emerges when growth responses from these experiments are considered in relation to daily intakes of SAA (Fig. 14.9). Considering the wide differences in dietary CP contents, ratios of methionine to cystine and ages of turkeys used, there appears to be a marked degree of homogeneity among the different data sets. This agreement is all the more significant in view of the widely held belief that empirical data obtained under one particular set of conditions are unlikely to have universal application. Irrespective of data source, the responses in Fig. 14.9 indicate that turkeys growing at about 30 g day-1 require 500 mg SAA

"O

Dietary lysine concentration (g kg-1)

Fig. 14.6. Daily weight gain of male (o) and female (•) broiler chicks in relation to total dietary lysine concentration. (From D'Mello, 1979; source of data: Thomas eta!., 1977. Reproduced with permission from ButterworthHeinemann Ltd.)

day-1, whereas older turkeys growing at 90 g day-1 require approximately 1700 mg SAA day The improved agreement between the data of Behrends and Waibel (1980) and Murillo and Jensen (1976) when responses are considered in relation to SAA intake (Fig. 14.9) may be attributed to variations in food intake caused by differences in the environmental temperatures used in the two studies.

Species

The amino acid requirements of different species of growing poultry are reviewed on a regular basis. When expressed as dietary concentrations, differences in requirements are evident, particularly for arginine. Thus, the arginine requirement is estimated to be 12.5 g kg-1 diet for broiler chicks and 16.0 g kg-1 diet for turkey poults (National Research Council, 1994). The question arises as to whether these differences reflect genuine variations in amino acid utilization. D'Mello (1979) addressed this issue at some length using evidence from studies specifically designed to compare amino acid utilization in young turkeys and chicks. With respect to arginine (Fig. 14.10) it was suggested that turkey poults and chicks respond similarly to different intakes of this amino acid. Potential growth rates in the turkey, however, are much greater and consequently responses occur to higher intakes of arginine. Food intake per unit of liveweight gain is higher in the chick than in the poult and these two factors together contribute to the much lower arginine requirement of the chick when this value is expressed in terms of dietary concentrations (D'Mello and Emmans, 1975). There is no evidence of any differences in the efficiency of arginine utilization between the two species. Any such difference would have been represented by two discrete response curves in Fig. 14.10. Interspecies similarities were later extended to isoleucine and valine responses for turkey poults and chicks (D'Mello, 1975) whereas in the case of the SAA (D'Mello, 1976), it was observed that data obtained with the laboratory rat also conformed with the responses seen in poultry (Fig. 14.11). The plateaux for the various sets of data indicate the maximum growth possible in the respective experiments with the animals and diets used (Stockland et al., 1973; Boomgaardt and Baker, 1973; D'Mello, 1973a, 1976).

The demonstration of strain differences in arginine utilization by chicks (Nesheim, 1968) is less readily explained and may represent an exception to the general rule. It should be noted that the strains differing in arginine requirements were selected on the basis of their responses to high-casein diets containing excess lysine. Under these conditions there is a clear difference in responses

"O

1050

Lysine intake (mg day-1)

Fig. 14.7. Daily weight gain and lysine intakes of male (o) and female (•) broiler chicks. (From D'Mello, 1979; source of data: Thomas et at., 1977. Reproduced with permission from Butterworth-Heinemann Ltd.)

Table 14.1. Published estimates of the requirements of turkeys (g kg 1 diet) for methionine + cystine. (From D'Mello, 1983.)

Reference

Age of turkey (weeks)

8-12 16-20

D'Mello (1976) Murillo and Jensen (1976) Potter and Shelton (1976) Potter et al. (1977) Potter and Shelton (1978) Potter and Shelton (1979) Beh rends and Waibel (1980)

  1. 3 11.0-12.0
  2. 0 - 10.0

whether these are considered in relation to dietary concentrations or daily intakes of arginine. But when an arginine-deficient amino acid mixture is used in place of casein, the strain differences in responses to this deficiency largely disappear. The absence of breed differences in arginine responses of commercial broiler stocks was

100 r

Dietary methionine + cystine concentration (g kg-1)

Fig. 14.8. The effects of dietary methionine + cystine concentration and age on daily weight gain in turkeys. (Source of data: Behrends and Waibel (1980), 1-4 (•) and 8-12 (■) weeks of age; Murillo and Jensen (1976), 8-12 weeks of age (□).)

demonstrated by Wilburn and Fuller (1975). Their studies with Cobb and Hubbard chicks, fed high-casein diets to accentuate any potential breed effects, indicated only minor differences when growth responses were considered in relation to dietary concentrations. Any discrepancies virtually disappeared when responses were plotted against arginine intake (D'Mello, 1979), suggesting that variations in food intake were primarily responsible for the differences in dietary requirements.

There is currently some interest in the amino acid requirements of genetically lean and fat chickens. In a study of SAA utilization, et al. (1993) were unable to distinguish between the two genotypes when growth was considered as a function of SAA intake, although lean chickens deposited these amino acids more efficiently in feather and body proteins. Food intake was depressed and feather synthesis enhanced in lean relative to fat chickens. In addition, Alleman et al. (1999) concluded that threonine utilization was very similar in both lines. However, Tesseraud et al. (1999) claimed that lysine utilization was more efficient in a low-fat line of broiler chickens than in a control line. Efficiency was assessed by plotting weight gain and muscle protein deposition against lysine intake. The reasons for this discrepancy await elucidation.

100 r

"O

400 800 1200 1600

Methionine + cystine intake (mg day1)

2000

Fig. 14.9. Daily growth rates of turkeys in relation to daily intake of methionine + cystine. (From D'Mello, 1983; source of data: Behrends and Waibel, 1980 (•); D'Mello, 1976 (■); Murillo and Jensen, 1976 (□); Potter and Shelton, 1978 (A); Potter and Shelton, 1979 (A); Potter etal., 1977 (o).)

400 800 1200 1600

Methionine + cystine intake (mg day1)

2000

Fig. 14.9. Daily growth rates of turkeys in relation to daily intake of methionine + cystine. (From D'Mello, 1983; source of data: Behrends and Waibel, 1980 (•); D'Mello, 1976 (■); Murillo and Jensen, 1976 (□); Potter and Shelton, 1978 (A); Potter and Shelton, 1979 (A); Potter etal., 1977 (o).)

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